The present invention relates to the improvement of a starter for starting an engine, and particularly relates to the improvement of a starter for starting an engine of a motor vehicle through the action of a speed reduction planet gear mechanism.
FIG. 3 shows a conventional starter which is for starting an engine and includes a speed reduction planet gear mechanism. The armature 300 of the DC motor of the starter comprises an armature core 301, an armature shaft 302, on the halfway portion of which the armature core is provided, and a commutator 303 fitted on the armature shaft at the rear portion of the armature and connected to an armature coil 304 provided on the armature core. A holder 305 for brushes located in contact with the commutator 303 is coupled to a rear cover 307 by bolts 306. A bearing 308 for supporting the armature shaft 302 at the rear end thereof is fitted in the recess of the rear cover 307. A plurality of permanent magnets 309a for applying a magnetic field to the armature 300 are secured on the inside circumferential surface of the yoke 309 of the DC motor. A front cover 311 fitted with the internal gear 310 of the speed reduction planet gear mechanism is fitted to the end face of the yoke 309. A spur gear 312 is formed on the armature shaft 302 at the front end thereof. A plurality of planet gears 313 are engaged with the internal gear 310 and the spur gear 312. Bearings 314 are fitted in the planet gears 313 and supported by pins 315 secured to a flange 316 constituting the arm of the speed reduction planet gear mechanism. An output rotary shaft 317 is secured to the flange 316. A sleeve bearing 318 is fitted in the boss of the internal gear 310 and supports the output rotary shaft 317. A sleeve bearing 319 is fitted in the recess of the rear portion of the output rotary shaft 317 and supports the armature shaft 302 at the front end thereof. A steel ball 320 is provided between the ends of the armature shaft 302 and the output rotary shaft 317 to transmit a thrust. Helical splines 321 are formed on the outside circumferential surface of the halfway portion of the output rotary shaft 317. The helical splines of the outer member 322a of an overrunning clutch 322 comprising the outer member, an inner member 322b and rollers 322c are engaged with the helical splines 321 so that the outer member is slidable backward and forward. A stopper 323 is provided on the output rotary shaft 317 at the front end thereof to restrict the quantity of the axial movement of a pinion 324 coupled to the inner member 322b of the clutch 322. A sleeve bearing 325 is fitted in the anterior part of the front cover 311 and supports the output rotary shaft 317 at the front end thereof. A lever 326 is provided with a pivot 326a at the plastic halfway portion of the lever and fitted to the actuator 328 of an electromagnetic switch 327 and the peripheral portion of the overrunning clutch 322 at the ends of the lever. A movable contact 329 is attached with an electric insulator 330 to a rod 331 fitted in a core 332 so that the rod is slidable backward and forward. A fixed contact 333 is secured by a nut 334 to a cap 335 made of an electric insulator. An electromagnetic coil 336 for moving the actuator 328 is provided on a plastic bobbin 337 and housed in a case 338. A lead wire 339 connects the fixed contact 333 to one of the brushes. A spring 340 is housed in the actuator 328 to push the overrunning clutch 322 through the action of the lever 326. A spring 341 for returning the actuator 328 is provided further.
The operation of the conventional starter is described in detail from now on. When an ignition switch not shown in FIG. 3 is turned on, the electromagnetic coil 336 of the electromagnetic switch 327 is energized to move the actuator 328 backward to push the rod 331 to put the movable contact 329 into touch with the fixed contact 333. As a result, the armature 300 is energized through the contacts 329 and 333, the lead wire 339 and the brushes so that the armature is rotated. The rotation of the armature 300 is transmitted to the overrunning clutch 322 through the spur gear 312 and the planet gears 313 so that the speed reduction planet gear mechanism makes the rotational speed of the clutch lower than that of the armature. At that time, the pinion 324 engaged with the clutch 322 is rotated. The actuator 328 being moved backward as mentioned above swings the lever 326 counterclockwise (as to FIG. 3) about the pivot 326a to slide the clutch 322 together with the pinion 324 forward in the axial direction thereof to engage the pinion with a ring gear formed on the peripheral portion of a flywheel mounted on the crankshaft of the engine not shown in FIG. 3. The engine is thus started. After that, the overrunning clutch 322 is disengaged from the pinion 324 because of the rotative action of the engine to the pinion, so that the pinion races.
Since the axis of the DC motor is not coincident with that of the electromagnetic switch 327, it is necessary that the installation space for the switch is provided in a part of the engine or a vehicle. For that reason, the layout of the engine in the vehicle is restricted. This is a problem. Since the front cover 311 is open at the ring gear of the flywheel of the engine, the dust entry preventing property of the front cover is low. This is another problem. Since the overrunning clutch 322 and the pinion 324 are coupled to each other, the number of the turns of the electromagnetic coil 336 of the electromagnetic switch 327 needs to be increased to cause a high electromagnetic force to move the clutch and the pinion together with each other in the axial direction thereof. For that reason, the size and weight of the electromagnetic switch 327 are augmented. This is yet another problem. Since it is difficult due to the constitution of the starter that the distance between the ring gear of the flywheel of the engine and the surface of the starter, which is mounted on the engine, is made larger than a certain value, the design of the part of the engine, which is located near the transmission of the vehicle, is restricted. This is yet another problem. Since a certain clearance needs to be set between the mutually-engaged helical splines of the outer member 322a of the overrunning clutch 322 and the output rotary shaft 317 in order to make it possible to slide the outer member and the shaft backward and forward relative to each other, the outer member becomes eccentric to the inner member of the clutch. For that reason, the overrunning clutch 322 cannot always function stably. This is yet another problem.